1. Field of the Invention
The field of the invention relates to plug valves, and in particular to lined plug valves of the type wherein a liner of Teflon or the like is interposed between the adjacent surfaces of the plug and plug receptive bore of the valve body.
2. Description of the Prior Art
This invention comprises a modification of the leakproof, rotary, plug-type fluid control valve of my U.S. Pat. No. 3,930,635*, assigned to the assignee of this application, which was an improvement on my U.S. Pat. No. 3,521,856*, also assigned to the assignee of this invention. FNT *A copy of this patent is submitted with this application.
The valve of this invention differs from the valve of U.S. Pat. No. 3,930,635 in that a buffering media is maintained, under continuous pressure which exceeds the pressure of the line media being controlled at all potential leak paths of the line media including the plug cavity when the valve is closed. The buffering media is also, in certain instances, utilized to automatically purge the plug cavity of the line media and then fill it with buffering media each time the valve is closed.
In my U.S. Pat. Nos. 3,930,635 and 3,521,856 the sealant was a heavy, viscid grease, a silicone grease, or caulk-like compound characterized by high viscosity and great resistance to dilution by the fluid line media being controlled by the valve. The sealant was not adapted to be introduced into the plug cavity, nor used as a purging agent when the valves were closed.